Iron interference in Mo determination in Mehlich-1 and Mehlich-3 soil extracts

Among the essential plant nutrients, molybdenum (Mo) has the lowest concentration in soils. A routine method for the determination of soil Mo availability is not yet established. Soil analysis methods have been tested but not one has been set to be used in a routine basis in Brazilian laboratories. Tropical soils are characterized by high Fe contents that may interfere in the soil Mo availability determination. This work aimed to evaluate the interference of Fe in the Mo determination in Mo standard solutions and in Mehlich-1 (M1) and Mehlich-3 (M3) soil extracts. The KI + H2O2 reaction method was used for Mo determination. Addition of Fe causes interference in Mo determination in Mo standard solutions using the KI + H2O2 reaction for dosage. Soil Mo determined by the KI + H2O2 method in M1 extracts were overestimated as compared to Mo determined in M3 extracts. The presence of NH4F in the Mehlich-3 solution seemed to be the reason for the difference